Multi-cavity sample cylinder with integrated valving

ABSTRACT

A system for obtaining a representative sample of a natural gas stream, particularly a stream which is at or below its hydrocarbon dew point temperature (H.C.D.P.). The preferred embodiment of the present invention contemplates a sample cylinder having a flexible isolation barrier and integrated valving to provide a controlled ingress of sample gas at nominal pressure differential. The system thereby avoids throttling of the sample gas and the inherent cooling problems associated therewith when the stream is at or below hydrocarbon dew point temperature. The flexible isolation barrier of the present invention is relatively inexpensive and is configured for quick and easy replacement, which may be routinely performed to insure sample integrity. Alternative embodiments of the invention contemplate a spherical sample cylinder configuration with flexible isolation barrier, as well as an improvement for piston-type sample cylinders to provide constant sample pressure.

PRIORITY CLAIM

The present application claims the benefit of U.S. Provisional PatentApplication No. 60/400,736, having a filing date of Aug. 2, 2002 listinginventor Donald A. Mayeaux.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to sampling of hydrocarbon fluid streamsand devices therefore, and in particular to a system particularlysuitable for obtaining a representative sample of a natural gas stream,which is at or below its hydrocarbon dew point temperature (H.C.D.P.).The preferred embodiment of the present invention contemplates a samplecylinder having a flexible isolation barrier and integrated valving toprovide a controlled ingress of sample gas at nominal pressuredifferential. The system thereby avoids throttling of the sample gas andthe inherent cooling problems associated therewith when the stream is ator below hydrocarbon dew point temperature. The flexible isolationbarrier of the present invention is relatively inexpensive and isconfigured for quick and easy replacement, which may be routinelyperformed to insure sample integrity. Alternative embodiments of theinvention contemplate a spherical sample cylinder configuration withflexible isolation barrier, as well as an improvement for piston-typesample cylinders to provide constant sample pressure.

GENERAL BACKGROUND OF THE INVENTION

Natural gas is a vital source of heat energy in the United States. Itsselling price is based on volume and heat content. The heat content isgreatly influenced by the presence of the heavy (higher molecularweight) components. These heavy components also have a large influenceon the gases physical properties, which in turn impact flow ratecalculations. The heat content and physical properties of gas areprimarily determined by calculations based on gas composition.

The gas composition is determined by analysis on gas obtained by one ormore of three means: spot sampling, composite sampling, and on stream(on line) analyzer sample systems. Spot sampling consists of extractinga natural gas sample at a point in time representing source gascomposition at that point in time. The sample is stored in a samplecontainer (sample cylinder).

Composite sampling consists of extracting very small increments ofnatural gas samples over a long period of time, usually one month, saidsamples being stored in a single sample container. The result is acomposite of a sample gas representing the entire quantity of sourcegas, which flowed through the pipeline during the sampling period.Sample containers containing stored spot or composite samples aretransported to a laboratory and analyzed for composition.

In the case of “on stream analyzer sample systems” a sample is withdrawncontinuously or semi-continuously and routed directly into to ananalyzer, usually a gas chromatograph, for real time analysis. It iswell known by the natural gas industry that it is very difficult toobtain a representative sample of a natural gas stream, which is at orbelow its hydrocarbon dew point temperature (H.C.D.P.).

The American Petroleum Institute (API) Manual of Petroleum MeasurementStandards, Chapter 14, Section 1 and Gas Processors Association's (GPA)Standard 2166, “Obtaining Natural Gas Samples for Analysis by GasChromatography”, are good references for sampling of natural gas. Bothorganizations recognize the difficulty in sampling natural gas with highH.C.D.P. The GPA Standard 2166 outlines eight methods for spot samplingwith sample cylinders. The API 14.1 standard provides furtherrecommendations on the use of these methods.

The standards refer to several sources of error. Some of the mostimportant are as follows:

-   -   1) Sampling a natural gas source containing liquid in any form.        i.e.—The source gas is at or below its H.C.D.P. temperature.    -   2) Sampling a natural gas source at an ambient temperature that        is below the H.C.D.P. temperature of the flowing gas source.    -   3) Throttling of the sample gas stream as it flows from the        source to a sample container or on stream analyzer, especially        if the throttling causes the temperature to drop (Joule-Thomson        cooling effect) to near or below the gas H.C.D.P.

The importance of proper treatment of natural gas samples that are nearor below their H.C.D.P. is the focus of the industry's attention,especially in light of the mining of natural gas from deeper reserveshaving higher H.C.D.P. temperatures and the increasing value of naturalgas.

Major problems with spot and composite sampling are the accumulation ofliquid in the sample container during the “purging” phase and depletionor accumulation of high molecular weight components during the samplefilling phase.

During the purging phase of sampling, sample lines from the source tothe sample container and the sample container itself are purged withsample gas to remove or displace residual gases. Most of all of theproblems addressed by the eight GPA Sampling methods are related to thepurging phase.

There are currently two basic types of sample containers (samplecylinders). One is the constant volume type, which is usually a smallsteel cylinder with fixed volume having valves at one or both sides. Thesecond type is a constant pressure sample cylinder. This is a smallsteel cylinder having an internal “floating” piston, end caps at bothcylinder ends, and valves in both end caps. The floating pistonseparates the internal cylinder volume into two cavities. The pressurein the two cavities is maintained at somewhat the same level by movementof the floating piston. For example, if the pressure in one cavity israised above that of the other cavity, the floating piston is moved inthe direction of the lower pressure cavity until the pressure in bothcavities is somewhat equilibrated. This type of sample cylinder wasdesigned to prevent “throttling” of sample gas.

After purging of exterior lines, pre-charge gas (gas stored at elevatedpressure in one of the cavities before actual sampling begins) isreleased slowly. When the “pre-charge” gas pressure drops below thesample supply pressure, the piston moves towards the pre-charge cavityend of the cylinder allowing the sample gas to enter the sample cylinderwithout throttling.

Several problems are associated with the use of this type of hardware.One such problem is that the friction of the piston seals can cause apressure difference of 20 to 30 PSI between the two cylinder cavities.The second is that the piston seals can harbor contaminates fromprevious samples. Cleaning is very difficult and time consuming. Theentry ports and valving designs in the end caps require purging and alsorepresent a source of sample composition distortion during the purgingphase.

Constant volume cylinders are difficult to clean between samples asrecommended by API and GPA standards. It is also difficult if notimpossible to verify if they are indeed clean after the cleaningprocess.

Further, prior art valves typically installed on sample cylinders areprone to becoming damaged during transportation. The valve knobs aremounted on slender stems, which protrude from the valve body. The stemsare often bent when cylinders are dropped or handled roughly. Valve stempacking leaks are also a common problem. Vibration and rough handlingduring transportation an also result in valves becoming partially openedthereby allowing fluids to leak out.

The prior art has therefore failed to provide a constant volume-typesample cylinder which is easy to clean and service, reliable inoperation, and effective in preventing throttling of the sample gas.

GENERAL SUMMARY DISCUSSION OF THE INVENTION

Unlike the prior art, the present invention provides a system forobtaining a representative gas sample with a sample cylinder whichallows for sampling with nominal pressure differential during sampling,so as to avoid the Jule-Thomson cooling effect, and thereby preventliquification of parts of the sample due to a drop to or belowhydrocarbon dew point pressure.

The preferred embodiment of the present invention contemplates a samplecontainer, which may be a cylinder, sphere, or other confiruation,having a flexible isolation barrier and integrated valving to provide acontrolled ingress of sample gas at nominal pressure differential.Throttling of the gas is thereby avoided.

Further, the flexible isolation barrier may be fabricated of an inert,relatively inexpensive, and easily handled material, and the cylinder isthereby designed for easy repair or replacement of the barriercomponent, which replacement may be routinely performed to insure sampleintegrity. Further, barriers of different materials may be changed outas required, depending upon the material in contact with the barrier.

In the preferred embodiment of the present invention, the samplecylinder is divided by the flexible isolation barrier, providing firstand second cavities, the first cavity for receiving a fluid sample, thesecond cavity for providing pressure means (via pre-charging)commensurate with the ingress pressure of the sample gas, to providecontrolled ingress of the sample gas into the first cavity.

An alternative embodiment of the present invention contemplates animprovement in piston-type sample cylinders to provide constant samplepressure, utilizing an improved valve ingress and discharge system toprovide a more controlled sampling than prior art piston cylindersystems.

It is therefore an object of the present invention to provide a samplecontainer having a flexible isolation barrier configured to receivesample fluids at nominal pressure differentials.

It is another object of the present invention to provide a method ofsampling gas utilizing a flexible isolation barrier system.

It is another object of the present invention to provide an improvementin piston-type sample cylinders, providing a pressure equalizationsystem to provide nominal pressure differentials during sampling.

It is another object of the present invention to provide a samplecylinder having a flexible isolation barrier which is easily and quicklychanged to prevent contamination, or to provide an alternative barriermaterial as required.

Lastly, it is an object of the present invention to provide a method andsystem for sampling gas at or near the hydrocarbon dew point temperaturewhich provides an accurate sample, while avoiding fluid formation due togas throttling.

BRIEF DESCRIPTION OF DRAWINGS

For a further understanding of the nature and objects of the presentinvention, reference should be had to the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich like parts are given like reference numerals, and wherein:

FIG. 1 is a schematic view of a sample cylinder with a flexibleisolation barrier attached in the middle.

FIG. 2 is a schematic view of a sample cylinder with a flexibleisolation barrier totally expanded in cavity 3, with cavity 3 volumeequaling zero and cavity 4 is at its maximum volume.

FIG. 3 is a schematic view of a sample cylinder with a flexibleisolation barrier totally expanded into cavity 4, with cavity 4 volumeequaling zero and cavity 3 is at its maximum volume.

FIG. 4 is a schematic view of a sample cylinder with a flexibleisolation barrier totally expanded in cavity 3, with cavity 3 volumeequaling zero and cavity 4 is at its maximum volume.

FIG. 5 is a schematic view of a sample cylinder of the head and bowldesign of the present invention, with the flexible isolation barrier isattached in the head and internal flow paths are shown schematically.

FIG. 6 is a schematic view of a sample cylinder of the head and bowldesign, with the flexible isolation barrier attached in the head andinternal flow paths, wherein the cavity 3 volume equals zero and cavity4 volume is at its maximum.

FIG. 7 is a schematic view of the sample cylinder of the head and bowldesign, with the flexible isolation barrier attached in the head andinternal flow paths are shown, and wherein cavity 4 volume is zero andcavity 3 volume is at its maximum.

FIG. 8 is a schematic, external view of the sample cylinder externalprofile with isolation barrier.

FIG. 9 is a side view of the flexible isolation barrier.

FIG. 10 is a top, cut-away view of the head of the system of the presentinvention, showing the integrated valves and some fluid passages, withthe valves shown in their closed position.

FIG. 11 is a side, cut-away view of the sample cylinder of the presentinvention, illustrating the purge and vent valves, and end view of inletvalve.

FIG. 12 is a flow diagram for the initial sample cylinder preparationprior to sampling gas.

FIG. 13 is a top view, cut-away view of head of the present invention,wherein integrated valves and some fluid passages are shown, with theinlet and vent valves shown in their open position, and the purge valveis shown in a closed position.

FIG. 14 is a side, cut-away view of the inlet valve of the samplecylinder of the present invention, showing passages from inlet valve tocavity 3, as well as the pin in hole passage and flexible isolationbarrier.

FIG. 15 is a close-up, cut-away view of the bowl rim and head area ofthe sample cylinder of the present invention.

FIG. 16 is a top, partially cut-away view of the head of the samplecylinder system of the present invention, illustrating the integratedvalves and some fluid passages, with the vent and inlet valves are in aclosed position, and the purge valve in a closed position.

FIG. 17 is a flow diagram illustrating the filling of the samplecylinder from a gas source.

FIG. 18A is a top view of the inlet port, inlet valve and purge valve ofthe head on the sample cylinder of the present invention, with the inletvalve and purge valve shown in closed position.

FIG. 18 b is a top view of the inlet port, inlet valve and purge valveof the head on the sample cylinder of the present invention, with theinlet valve shown in a closed position, and the purge valve shown in anopen position.

FIG. 18 c. is a top view of the inlet port, inlet valve and purge valveof the head on the sample cylinder of the present invention, with theinlet valve shown in a open position, and the purge valve shown in anclosed position.

FIG. 19 is a side, partially cut-away view of the sample cylinderflexible isolation barrier of the present invention totally collapsedagainst head surface, showing cavity 3 volume at zero, with cavity 4volume is at its maximum.

FIG. 20 is a flow diagram of SAMPLE CYLINDER illustrating a sample beingwithdrawn to an analyzer.

FIG. 21 is a schematic of a sample cylinder having two flexibleisolation barriers situated therein.

FIG. 22 is a schematic of a sample cylinder having two flexibleisolation barriers situated therein, and a mechanical restraint portionhaving openings to permit fluid flow.

FIG. 23 is a schematic of a sample cylinder having two flexibleisolation barriers situated therein, and a mechanical restraintpartition without openings.

FIG. 24 is a side, partially cut-away view of an off-the-shelf constantvolume cylinder equipped with a flexible isolation barrier and valving.

FIG. 25 is a flow diagram of an off-the-shelf constant volume cylinderequipped with a flexible isolation barrier and valving.

FIG. 26 a is a side, exploded view of a valve assembly-exploded.

FIG. 26 b is a side, partially cut-away view of an assembled Valveassembly.

FIG. 27 is a side, partially cut-away view of a constant volume samplecylinder with the flexible isolation barrier liner of the presentinvention.

FIG. 28 a is a top, partially cut-away view of a valve showing the knob,knob lock, and flat face seal, wherein the knob is screwed into head.

FIG. 28 b is a top, partially cut-away view of a valve showing the knob,knob lock, and flat face seal, with the knob unscrewed from the head.

FIG. 29 a is a top, partially cut-away view of the knob and knob lock.

FIG. 29 b is a close-up, partially cut-away, side view of the knob lockwith slots.

FIG. 29 c is a close-up, side view of the knob lock.

FIG. 30 is a side, partially cut-away view of head, bowl, flexibleisolation barrier, retention ring, and o-ring of the present invention.

FIG. 31 is a side, partially cut-away view of the head, inlet valve, pinand hole for the flexible isolation barrier support, and the flexibleisolation barrier.

FIG. 32 is a schematic of the cylindrical sample container with theflexible isolation barrier attached at one end.

FIG. 33 is a schematic view of the spherical sample container with theflexible isolation barrier attached near its middle.

DETAILED DISCUSSION OF THE INVENTION Sample Cylinder Device

Referring to FIGS. 1–4, the first invention consists of a cylinder 1forming the body of the unit, the cylinder having a chamber formedtherein having a flexible isolation barrier 6 attached therein (FIG. 1).Flexible isolation barrier 6 divides the internal volume of the cylinder1 into two sections or cavities (cavity 3 and cavity 4). Inlet valve 2and purge valve 13 installed at each end of the cylinder 1 provide fluidcommunication between each of the two cavities and the exterior of thecylinder 1.

By first opening inlet valve 2 and then allowing a source of gas(pre-charge gas) to flow into cavity 4 by way of purge valve 13, theflexible isolation barrier 6 is moved toward cavity 3 thereby displacingthe residual gas in cavity 3. When all of the gas is displaced, theflexible isolation barrier 6, being a thin and flexible material,conforms to the interior of the section of sample container formerlycomprising cavity 3.

The volume of cavity 3 is now essentially zero (FIG. 2). After closinginlet valve 2, the cylinder 1 may be disconnected from the pre-chargegas source and brought to a field location where source gas is to besampled. Purge valve 13 may be closed prior to disconnect if desired inwhich case the cavity 4 remains pressurized with pre-charge gas. This insome cases may be desired. In other cases, cavity 4 is depressurized toatmospheric pressure.

A source of gas to be spot sampled is first connected to purge valve 13.Opening purge valve 13 pre-charges cavity 4 to a pressure about equal tothe source pressure. Depending upon the pre-charge gas pressure incavity 4, gas flows from the source gas to cavity 4 or from cavity 4 tothe source gas. Purge valve 13 is now closed and the source gas is nowdisconnected from purge valve 13 and connected to inlet valve 2. Inletvalve 2 is then opened.

Source gas will not flow initially through inlet valve 2 since thepre-charge pressure is equal to the source pressure at inlet valve 2.Purge valve 13 is now opened partially allowing pre-charge gas fromcavity 4 to exit and flow to the atmosphere. As the pressure in cavity 4tends to lower by venting in this manner source gas enters cavity 3through inlet valve 2, the flexible isolation barrier 6 is moved towardcavity 4 which is now reducing in volume, but whose pressure is heldconstant at source pressure by the action of the flexible isolationbarrier 6 movement.

The pressure differential between the two cavities is essentially zerosince the flexible isolation barrier 6 material requires only amicroscopic force to flex. During the filling process through inletvalve 2, the source gas is not throttled, but rather its flow iscontrolled by the egress of the flexible isolation barrier 6, which inturn is controlled by the flow rate of pre-charge gas through purgevalve 13.

When the pre-charge gas is sufficiently discharged, the flexibleisolation barrier 6 conforms to the interior surface of the formercavity 4, as shown in FIG. 3, and cavity 4 volume is essentially zero.Inlet valve 2 is closed and the sample container can now be brought to alaboratory for analysis of the sample gas. Purge valve 13 may be closedto insure that in the event of an flexible isolation barrier 6 failure,sample gas would not be vented through purge valve 13. However,functionally it does not need to be closed.

To analyze the sample gas in the cylinder 1, the analyzer sample systemis connected to inlet valve 2. By opening inlet valve 2 sample gas flowsto the analyzer. The sample gas pressure of cavity 3 will fall as samplegas flows out of it. If it were desired to control the cavity 3 pressureat a specific level then a source of auxiliary gas is connected tocavity 4 by way of purge valve 13. The auxiliary gas pressure ismaintained by external means at the sample gas pressure desired incavity 3. In a manner similar to that which occurred during the filingprocess auxiliary gas will fill cavity 4 as sample gas exits inlet valve2 and the flexible isolation barrier 6 will retreat into cavity 3 untilthe cavity 3 volume is essentially zero as shown in FIG. 4.

The preceding describes the basic concept of a “constant pressure samplecylinder” construction by use of an flexible isolation barrier 6. Theaforementioned (figures) are more indicative of fluid flow paths then ofspecific mechanical design. FIG. 5 show that a cylinder 1 may bedesigned such that all valving and porting is located at one end of thecylinder 1. This makes it easier to manufacture the cylinder 1 andsubstantially improves performance by minimizing the volume of sourcegas required for purging.

FIGS. 5–7 reflect the fluid flow path and FIG. 8 indicates theapproximate physical location of the valves 2, 13, and 14, inlet port10, and vent port 11 relative to the flexible isolation barrier 6 andcavities 3 and 4, wherein cavity 3 is situated interior isolationbarrier 6, and cavity 4, exterior, the isolation barrier 6 having first,interior and second, exterior sides, in this application.

With this arrangement, (refer to FIGS. 5, 6, and 7) the pre-charging andsample filling of the cylinder 1 is as follows. The “vent” port 11 isconnected to a pre-charge gas source. Purge valve 13 is closed, ventvalve 14 open, and inlet valve 2 open. The inlet is at atmosphericpressure. By external valving means, pre-charge gas is admitted tocavity 4 by way of vent valve 14. The flexible isolation barrier 6 ismoved toward cavity 3 displacing residual gas in cavity 3. The residualgas is vented from the cavity through inlet valve 2.

When essentially all of the residual gas is expelled in this manner andthe flexible isolation barrier 6 conforms to the former cavity interiorsurfaces (FIG. 6), inlet valve 2 is closed, vent valve 14 is closed, andpurge valve 13 remains closed. Cavity 3's volume is essentially zero andcavity 4, whose volume occupies essentially all of the cylinder 1internal volume, is now filled with pre-charge gas. The pre-charge gaspressure can be very low (approximately 100 PSI); the exact pressuredepends on the flexible isolation barrier 6 flexibility. It is notessential to retain the pre-charge gas pressure in cavity 4. Thecylinder 1 can now be transported to a field location of source gas tobe sampled.

The source gas is connected to the inlet port 10 and purge valve 13 isopened. The source gas is allowed to flow into cavity 4 by openingexternal valving in the source gas connecting line (not shown). Aftercavity 4 is pre-charged in this manner until its pressure is equal tothe source gas pressure, purge valve 13 is closed and inlet valve 2 isopened. Source gas cannot flow into cavity 3 by way of inlet valve 2until vent valve 14 is opened and pre-charge gas from cavity 4 isallowed to exit by way of vent valve 14 and vent port 11 to theatmosphere. Vent valve 14 is now opened and as previously described, theflexible isolation barrier 6 retreats into cavity 4 allowing source gas(sample gas) to flow into cavity 3 without throttling occurring.

All external sources of throttling are removed, such as the opening ofvalves and the pre-charge exit flow is kept to a minimum rate so as notto create a pressure drop in the source gas connecting piping orinternal passages of the cylinder 1. When essentially all of thepre-charge gas is expelled from cavity 4 (FIG. 7) and source sample gasfills cavity 3, the flexible isolation barrier 6 conforms to theinterior surfaces of former cavity 4 completing the filling process,then valves 2, 13, and 14 are closed. Cylinder 1 may now be disconnectedfrom the source gas and transported to a laboratory for analysis.

At the laboratory or analyzer location, the analyzer's sample system isconnected to the “inlet port” 10. Inlet valve 2 is opened and sample gasfrom cavity 3 is allowed to flow into the analyzer sample system. Theflow rate is controlled by the analyzer sample system (not shown). If itis desired to maintain the gas pressure at a specific level in cavity 3,then as previously described, an auxiliary gas, applied to cavity 4 byway of vent valve 14, can be used to maintain the desired pressure.There are many variations of the purging, pre-charging, filling, andsample extraction from the cylinder 1 for analysis. The foregoingexplanation describes the general spirit of hardware design and gasflow.

Cylinder with Integrated Valves

Continuing with FIGS. 7–11, another important aspect of this inventionis the specific hardware design. For example, inlet valve 52, purgevalve 58 and vent valve 59 (FIGS. 8, 9, 10, and 11) are integrated intothe head 8 as well as the inlet port 10 and vent port 11. Inlet valve 52is designed into this structure such that when it is in a closedposition there is essentially zero volume between the flexible isolationbarrier 6 when fully retracted into cavity 3, (FIGS. 10 & 31), and inletvalve 52.

That means that cavity 3, which will ultimately contain the sample gasis essentially zero and therefore does not need to be purged. Recallthat great sources of problems and errors occur during the purging ofsample containers of prior art. An object of this invention is to reduceor eliminate the source of purging errors by eliminating the requirementfor purging the sample gas containing cavity.

Internal passages also provide for sample gas flowing into the inletport 10 from an outside source to sweep or purge the volume on theupstream side of inlet valve 52 (all volume between the inlet port 10and inlet valve 52). Refer to FIGS. 11, 13, & 14. Therefore in theaforementioned description of when source sample gas is flowing throughthe inlet port 10 and purge valve 58 to pre-charge cavity 4, essentiallyall of the volume upstream of inlet valve 52 is purged. In othervariations of the invention's design, gas, which is removed from cavity4 to allow filling of cavity 3, will be contained in a third cavity(cavity 16) [FIGS. 21, 22, and 23].

This design “measures” the amount of source gas used for purging in thesense that pre-charging of cavity 4 requires a specific volume ofpressurized gas. If external piping should require additional purging,then the pre-charge gas can be vented by opening vent valve 59. Ventvalve 59 is then closed and the pre-charging step repeated as many timesas required. Prior art hardware does not limit the purging; therefore,technicians are prone to excessive purging which can result in samplecomposition distortion errors.

In another variation of this invention cavity 16, formed by flexibleisolation barrier 15 (FIG. 21) is filled with an inert or non-harmfulgas. During the purging of the external sample delivery and cylinder 1internal passages flexible isolation barrier 6 is fully collapsed and byadmitting sample gas into cavity 4 by way of valve 13. At this point,cavity 3 has essentially a zero volume. During the filling of cavity 3with sample gas, the gas from cavity 16 is released allowing cavity 4 todepressurize. In that case only non-harmful gas is released to theatmosphere. Potentially harmful gas in cavity 4 may be disposed of at alater time in a safe area.

Initial Cylinder Preparation Prior to Sampling Gas

Cylinder 1 is connected to a gas source 87 and four way valve 90 asshown in FIGS. 12, 13, 14, and 15. With a new or clean flexibleisolation barrier 6 installed in cylinder 1, vent valve 59 and purgevalve 58 are closed, inlet valve 52 is opened and valve 90 is actuatedin a position in which its internal flow is represented by solid lines(i.e.—no flow through dashed lines).

Vent valve 59 is then opened (FIG. 13) allowing source gas 87 (FIG. 12)to flow through pressure regulator 88 line 89 into port 90 a and out ofport 90 b of valve 90, through line 99 into port 11, passage 64, ventvalve cavity 60, passage 76, into head/bowl annulus 70 (FIG. 15), frit74, passage 75 an into cavity 4.

This causes flexible isolation barrier 6 to fold up thereby forcing gasfrom cavity 3 through passage 66 (FIG. 14) and passage 65, into inletcavity 51 passage 81, inlet port 10, line 98, entering valve 90 at port90 d and exiting through port 90 c and then to the atmosphere or a safevent 91. When flexible isolation barrier 6 is completely collapsed andthe volume of cavity 3 is essentially zero, then vent valve 59 and inletvalve 52 are closed. The only remaining gas in cavity 3 is themicroscopic amount (approximately 0.005 cubic centimeters) trappedbetween the flexible isolation barrier 6 and inlet valve ball, FIGS. 10,14, and 16, in passages 66 and 65.

This small volume of trapped gas, usually at or near atmosphericpressure, is diluted when cavity 3 is later filled with sample gas whichproduces an insignificant amount of contamination. If in special caseseven this small amount of contamination cannot be tolerated, then atthis point in time, cavity 3 is filled with helium then vented until itsvolume is again essentially zero (approximately 5 micro liters). Thisdilutes the trapped gas, depending on the helium gas pressure suppliedto cavity 3, by a factor of approximately one million to one. Thisdilution step is performed by rotating valve 90 to its second positionwherein its internal flow is indicated by dashed lines (FIG. 12). Inletvalve 52 and vent valve 59 are opened allowing source gas 87 to flowthrough regulator 88, line 89 into port 90 a and exit of port 90 d intoline 98, inlet port 10, passage 81, cavity 51, passage 65, passage 66into cavity 3. The flexible isolation barrier 6 expands forcing gas fromcavity 4 to flow through passage 75, frit 74, annulus 70, passage 76,vent valve cavity 60, passage 64, vent port 11, line 99, into port 90 b,out of port 90 c to the atmosphere or safe vent area 91.

When flexible isolation barrier 6 is fully expanded and the volume ofcavity 4 is essentially zero and the volume of cavity 3 is at itsmaximum, valve 90 is actuated to its former position wherein itsinternal flow is indicated by solid lines. Supply gas 87 again flowsinto cavity 4 and the gas contents of cavity 3 flows to the atmosphereor safe vent area 91 as previously described. When flexible isolationbarrier 6 is fully collapsed and the volume of cavity 3 is essentiallyzero, then inlet valve 52 and vent valve 59 are closed and lines 98 and99 disconnected from cylinder 1. Cylinder 1 is now ready to be utilizedfor obtaining a gas sample.

Sampling a Gas Source

With vent valve 59, inlet valve 52, and purge valve 58 closed, line 84(FIGS. 14, 15, 16, 17, and 19) is connected to cylinder 1 inlet port 10.Valve 85 and purge valve 58 are opened allowing gas from source 83 toflow through valve 85, line 84 inlet port 10, passage 81, inlet valvecavity 51, passage 63, purge valve cavity 54, passage 100, annulus 70,frit 74, passage 75, and into cavity 4. Gas flows into cavity 4 untilits pressure is equal to the gas source 83 pressure. The filling ofcavity 4 in this manner has swept or purged the external sample deliverysystem, inlet port 10, passage 81, and inlet valve cavity 51 with samplegas.

A representative sample of the gas source 83 is present in inlet valvecavity 51. Purge valve 58 is closed, then inlet valve 52 and vent valve59 are opened. Gas from source 83 then flows into inlet port 10, passage81 (FIGS. 11, 13, 14, 15, and 17), inlet valve cavity 51, passage 65,passage 66, into cavity 3. Flexible isolation barrier 6 unfolds and gasfrom cavity 4 flows through passage 75, frit 74, annulus 70, passage 76,vent valve cavity 60, passage 64, vent port 11, then to the atmosphereor a safe area.

Volume between the collapsed flexible isolation barrier 6 and ball 49 ofinlet valve is essentially zero (approximately 5 micro liters) cavity 3requires no purging. That eliminates the largest source of samplingerror in filling sample gas cylinders.

If the residual volume is excessive for some rare applications, it maybe diluted with helium during the pre-charging of cavity 4 as previouslydescribed. In the case of natural gas wherein the analysis is typicallyperformed by Gas Chromatographs which utilize Helium as a carrier gas,the Helium will not be detected. In that case, all components of thesample gas are normalized to a total of 100%. Normalizing in this manneris a common practice.

Inlet valve 52, and vent valve 59 are then closed and line 84 of theexternal sample delivery system is disconnected. Cylinder 1 may now betransported to a laboratory for analysis of its sample gas contents.During the filling of cavity 3, throttling of the sample gas was avoidedas a means for controlling the gas flow rate. Instead the gas flow rateentering cavity 3 was actually controlled by the flow rate of gas beingvented from cavity 4 through vent valve 59. This process is ideal inseveral ways. First, even though throttling were to occur in theinternal passages of cylinder 1, leading into cavity 3, and theresulting Joule-Thomson cooling effect were to cool the gas below itsdew point resulting in condensation, it would not impact the compositionof gas in cavity 3. This is because all of the gas entering inlet valve52 passes into cavity 3.

This eliminates the problems caused by the purging of prior artcylinders. Secondly, the Joule-Thomson cooling effect from throttling ofvent valve 59 results in cooling of gas vented from cavity 4. This doesnot result in the cooling of cylinder 1 or the gas being sampled.

Third, even though the entire Joule-Thomson cooling effect were appliedto cylinder head 8 when releasing gas contents pressurized at 2000 PSIthe net result is less than 0.1 degree Fahrenheit change in thistemperature of head 8.

Removing Sample Gas from the Cylinder

Sample line 94 (FIG. 20) is connected to inlet port 10 and analyzer 95.When inlet valve 52 is opened, gas flows from cavity 3 through passage66 (FIG. 14), passage 65, inlet valve cavity 51, passage 81, inlet port10 and line 94 to analyzer 95. Sample flow and pressure regulationcomponents integral to analyzer 95 are not shown.

Optionally a source of gas may be utilized to maintain a constantpressure in cavity 3 as it discharges into the analyzer. To accomplishthis, a gas source 92 (FIG. 20) supplies gas through pressure regulator96, line 93 to vent port 11. Opening vent valve 58 allows the gas sourceto then flow into cavity 4 by paths previously described. The pressureof cavity 3 is controlled by the pressure of gas in cavity 4 sinceflexible isolation barrier 6 deflects in response to any difference inpressure between the two cavities. Upon completion of analysis, lines 93and 94 may be disconnected after first closing inlet valve 52 and ventvalve 58.

Cylinder Design Variations

There are other variations of methods for utilizing the inventions aswell as hardware design that are obvious to one skilled in this art. Forexample, FIGS. 1 & 33 show the attachment of the flexible isolationbarrier 6 at two different points within the interior of the cylinder 1:one at the top (FIG. 32) and one at the approximate center (FIG. 1).Another variation is shown in FIG. 33 whereby the cylinder 1 is somewhatspherical as opposed to a cylindrical shape.

In FIG. 21, flexible isolation barriers 6 and 15 are shown. By use ofappropriate valving a duplicate sample can be obtained in cavities 16and 3 while using cavity 4 for pre-charging. This is useful foranalyzing one sample and “retaining” a second sample for future analysisin the event of a disputed analysis in custody transfer applications.There may be many other reasons to obtain duplicate samples or twosamples of different sources or same source at two different conditionsor periods of time. Alternatively, vented sample fluids could beselectively released into the second cavity or chamber via a rupturedisc.

In FIG. 22, a mechanical restraint 17 limits the travel of flexibleisolation barriers 6 and 15. The mechanical restraint 17 has passages,which permits pre-charge gas to pass between cavities 22 and 23. Thispermits the volume of cavities 3 and 16 to become “fixed.”

In FIG. 23, a partition 25 physically divides the cylinder 1 into twosections internally. Pre-charge gas cannot flow through partition 25.Pre-charge gas can only flow between cavities 27 and 26 via transfervalve 24. This physical arrangement provides a wide choice of purging,pre-charging, filling, and discharging techniques or methods. It isessentially two independent sample containers. Vent valve 13 and ventvalve 35 provide means for gas to flow into and out of cavities 27 and26 respectively.

The aforementioned hardware of FIGS. 1–8 can be used to sample sourcegas at atmospheric pressure or sub-atmospheric pressure. This isaccomplished by evacuating cavity 4 with cavity 3 at zero volumecondition. When the “inlet valve” 2 is opened, low-pressure gas from anexternal source is drawn into cavity 3 by the action of the flexibleisolation barrier 6 retreat toward cavity 4. When it is desired todischarge the sample gas for analysis, cavity 4 can be pressurized todisplace the flexible isolation barrier 6 thereby pressurizing samplegas in cavity 3 which then can be discharged through inlet valve 2 (FIG.1).

When pre-charging, purging and filling cavity 3 and 27 in the upperportion of the cylinder 1 in FIG. 23, it is possible to “vent” thepre-charge gas into cavity 26 during the filling of cavity 3. This wouldeliminate the discharge of sample gas to the atmosphere. This is veryimportant, especially when sampling toxic gas. There are othervariations of the hardware design and techniques for their use, whichshould be obvious to those skilled in the art.

Another invention is the use of a flexible isolation barrier 6 in asample container of the “constant volume” type. The constant volumesample containers have been in use for many years for sampling gases andliquids. In FIG. 24 it can be seen that a conventional constant volumecylinder 32 has been outfitted with a plug 31 at the lower and at theother end with a special valving arrangement having an flexibleisolation barrier 6 attachment. As can be seen in the flow diagram ofFIG. 25, the valving and cavity arrangement form flow paths and storagecavity relationships equal to that of the “head 8” and “bowl 9”arrangements previously discussed.

Therefore, constant volume cylinders of prior art may now be retrofittedas shown in FIG. 24 and used as previously described for the “head 8”and “bowl 9” design. New constant volume cylinders of prior art designmay also be fitted and used as described. The valving arrangement ofFIGS. 24 and 25 is designed such that the pre-charging gas cavity 4sweeps (purges) the entire inlet port 10 and inlet valve 2 area in asimilar manner as previously descried for the “head 8” and “bowl 9”designs. It can be readily seen that liquids, slurries, liquefied gasesand other fluids may be sampled in a similar manner as previouslydescribed for gases. As shown in FIG. 27, the flexible isolation barrier6 can be attached to a constant volume sample cylinder 106 in a mannerthat it functions as a liner or barrier to isolate sample fluidscontained in said sample cylinder from the interior sample cylinderinterior surfaces.

The flexible isolation barrier 6 is constructed of a thin flexiblematerial, which is preferably inert and does not permeate any fluids ofinterest into the sample gas or pre-charge gas. Although many materialsmay be utilized for construction of flexible isolation barrier 6, amaterial of choice utilizes “Tedlar”® brand polyvinyl fluoride, which ismanufactured by Dupont. It has been utilized for many years in theconstruction of sample bags for collecting and storing environmentalsamples and therefore has a good “history”. Many other polymericmaterials and elastomers may also be used. To reduce or eliminatediffusion of small molecules (such as Helium or Hydrogen) through theflexible isolation barrier 6, the material of construction may be coatedor metalized.

By using the flexible isolation barrier 6 in a cylinder 1 construction,as previously described, the “sample fluid” does not contact theinterior surface of the cylinder 1 bowl 9. Only a very small amount ofsurface in the “head 8” is contacted by sample fluid. When the cylinder1 is designed as previously shown, the “head 8” is bolted or screwed tothe “bowl 9”.

When the “head 8” and “bowl 9” are unbolted (or unscrewed) and separatedthe flexible isolation barrier 6 is easily accessed for inspection orreplacement. The interior surface of the “head 8”, valving, and fluidpassages may be easily accessed for cleaning. In practice, the flexibleisolation barrier 6 may be removed and replaced with a new clean one.

The “head 8” is easily cleaned in a fluid bath by either wiping oranother suitable means. This arrangement eliminates the cleaning problemassociated with prior art constant volume and constant pressurecylinders.

The entry points to cavity surfaces of the cylinder 1 are designed toprevent damage to the flexible isolation barrier 6 when made to conformto an interior surface at said entry points. The entry point consists ofeither one or more small holes or a porous material such as sinteredplastic or metal. A third preferred method of entry/exit passage is apin in hole construction as can be seen in FIGS. 14 and 16. In that casethe annulus (passage 66) is formed around the exterior pin 67 surfaceand the interior of the hole that the pin 67 is pressed in.

It can be readily seen that a change of hardware arrangement is possiblewithout changing the spirit of the described invention. Valving may bepositioned at either or both ends to effect the same or similar flowarrangement without changing the spirit of the invention.

In summary, the use of flexible isolation barrier 6 and cavities asshown in general, combined with the filling, pressurizing, evacuation,and discharge of fluids in the sample cylinder 1 made possible by theaforementioned hardware, provides by intention, a vast number of optionsfor sampling fluids.

Constant Pressure Sample Cylinder

Prior art designs of constant pressure sample cylinders have valvingintegrated into one or both end pieces of the sample cylinder. Thevalving of prior art constant pressure cylinders require large amountsof fluid to purge the volume upstream of the inlet valve. The valvingalso does not provide a near zero volume space between the inlet valveand the floating piston.

This requires purging of said space to remove residual fluid. Integratedvalving, as previously described for application to flexible isolationbarrier equipped cylinders may be applied to current art constantpressure cylinders having floating pistons.

The purge (pre-charge) valve and inlet valve can be designed in such amanner that gas flowing into the pre-charge end of the cylinder sweepsor purges the entire external sample delivery system and all internalpassages upstream of the inlet valve. This is similar to therelationship between inlet port 10, purge valve 58, and inlet valve 52shown in FIG. 10. The floating piston and internal cylinder head innersurface can the be designed in a manner that produces essentially zerodead volume between the floating piston and inlet valve when thefloating piston is fully retracted to the integrated valve end of thecylinder. This is similar to the relationship between flexible isolationbarrier 6, and inlet valve 52 (FIG. 14).

Integrated Valve

Inlet valve 52, purge valve 58, and vent valve 59 (FIG. 10) are designedto provide a low internal valve volume, zero dead or unswept volume,protection against stem damage, and a backup seal to prevent fluidleakage during transportation.

The three aforementioned valves are of the same design, each having onlyslight variations to accommodate their specific functions. Therefore thefollowing description of inlet valve 52 design is also applicable to thepurge valve 58 and vent valve 59 designs. Inlet valve assembly 52consists of (FIG. 26A), ball 49, o-ring 48, valve stem 45, recessed stemtip 97 to receive ball 49, o-ring groove 102 to receive o-ring 48, malethreads 47 a, shoulder 50, screw 46, spring 44, knob lock ring 42 havinga hole 43, pin 41, o-ring 40, knob 36, male thread 38, o-ring groove 39to receive o-ring 40, screw 37 a having a dog point tip 37 c, and screw37 b having a dog point tip 37 d.

Inlet valve assembly 52 is assembled as shown in FIG. 26 b. Knob lock 42is fastened to stem 45 by the insertion of pin 41 through hole 43 andhole 104. Inlet valve is installed in Head 8 as shown in FIGS. 27, 28 a,and 29 b.

As shown on FIG. 28A and FIG. 10, the inlet valve assembly 52 is engagedin the fully closed position with ball 49 providing a seal against seat56 (FIG. 10). The rotation of valve stem 45 in conjunction with malethread 47 a and female thread 47 b provide the linear travel required toseat and unseat ball 49 against seat 56. Male threads 38 a and femalethreads 38 b are shown fully engaged in FIG. 28 a.

O-ring 40 in contact with surface 5 provides a seal for stem 45. Shouldthe aforementioned seal fail, then fluids will be contained by thesecondary flat faced seal formed by o-ring 40 in contact with surface 5(FIG. 28 a). In the position shown in FIG. 28 a and FIG. 10, knob 36 isnot mechanically engaged to stem 45. Therefore any hard blows to knob 36resulting from rough handling would not either damage stem 45 nor rotatestem 45 in a manner which would result in disrupting the seal formed byball 49 against seat 56. This is a safety feature and one which protectsthe environment.

To actuate inlet valve 52 to its open position (FIGS. 28 b and 13)requires first rotating knob 36 to disengage male threads 38 a fromfemale threads 38 b. After the threads are disengaged, spring 44 forcesknob 36 away from head 8. Knob 36 is then rotated in any direction untildog point tips 37 c and 37 d of screws 37 a and 37 b enter slots 82 aand 82 b (FIGS. 28 b, 29 a, 29 b, and 29 c) of knob lock 42. Thismechanically locks knob 36 to stem 45. Thereafter rotation of knob 36will actuate valve 52 to its open and closed positions. To protect thevalve stem 45 from damage and to contain any fluid leaks which mightoccur from failure of stem seal formed by o-ring 48 and surface 103(FIGS. 10, 28 a and 28 b) the knob is pushed inward until male threads38 a contact female threads 38 b at which point dog points 37 c and 37 dare out of slots 82 a and 82 b and knob 36 is mechanically disengagedfrom stem 45. Rotating knob 36 will not rotate stem 45 at this point.

Male threads 38 a are then engaged tightly into female threads 38 b(FIG. 28 a) which provides protection for stem 45 and restores o-ring 40seal to surface 5 (FIG. 10).

Replacing the Flexible Isolation Barrier

Instead of using an elaborate cleaning procedure to eliminatecontaminates on the cylinder interior surfaces 105 (FIG. 30) as requiredby current art cylinders the flexible Isolation Barrier 6 is removed andreplaced with a clean one. This is accomplished by unscrewing bowl 9from head 8 and removing the flexible isolation barrier retention ring69 with attached flexible isolation barrier 6 and o-ring 78 as shown inFIG. 30. O-ring 78 is then removed from retention ring 69 after flexibleisolation barrier 6 is removed from retention ring 69. A clean flexibleisolation barrier 6 is then inserted over retention ring 69 and o-ring78 is installed over flexible isolation barrier 6 and retention ring 69.The flexible isolation barrier 6, retention ring 69, and o-ring 78assembly is then lowered into bowl 9 and head 8 replaced by screwing onbowl 9. O-ring 101 seals head 8 and bowl 9. As shown, the isolationbarrier 6 is formed to provide a mouth M to provide the opening to theinterior containment area for the sample gas.

O-ring 78 forms a seal (see FIG. 15) between bowl rim 77, head innersurface 80, retention ring shoulder 79 and flexible isolation barrier 6.Shoulder 79 is forced downward by head surface 80 causing o-ring 78 todisplace against all of the aforementioned sealing surfaces.

Referring to FIGS. 1–33, the elements of the invention are summarized asfollows:

Description Element # Container for Gases  1 Inlet Valve A  2 Cavity A 3 Cavity B  4 Surface  5 Flexible Isolation Barrier A  6 Vent Valve  7Head  8 Bowl  9 Inlet Port  10 Vent Port  11 Inlet Valve A Knob  12Purge Valve  13 Vent Valve  14 Flexible Isolation Barrier-B  15 Cavity C 16 Mechanical Restraint  17 Partition  18 Cavity D  19 Inlet Valve C 20 Cavity B-1  22 Cavity B-2  23 Transfer Valve  24 Solid Partition  25Cavity D  26 Cavity E  27 Purge Valve Knob  28 Vent Valve Knob  29Integrated Valve Assembly  30 Plug  31 Constant Volume Cylinder  32Purge Valve Assembly  33 Vent Valve Assembly  34 Purge Valve  35 InletValve Knob  36 Knob Retention Screw  37a Knob Retention Screw  37b KnobRetention Screw Tip  37c Knob Retention Screw Tip  37d Knob Male Threads 38a Knob Female Threads  38b O-ring Groove  39 O-ring  40 Knob Lock Pin 41 Knob Lock Ring  42 Hole  43 Spring  44 Inlet Valve Stem  45 Screw 46 Male Stem Thread  47a Female Stem Thread  47b O-ring  48 Ball  49Stem Shoulder  50 Inlet Valve Cavity  51 Inlet Valve Assembly  52 PurgeValve Stem  53 Purge Valve Cavity  54 Ball  55 Inlet Valve Seat  56Purge Valve Seat  57 Purge Valve Assembly  58 Vent Valve Assembly  59Vent Valve Cavity  60 Vent Valve Ball  61 Vent Valve Seat  62 InletValve/Purge Valve Passage  63 Vent Valve/Vent Port Passage  64 InletValve/Cavity 3 Port Passage  65 Cavity 3 Port Passage  66 Cavity 3 PortPassage Pin  67 Cross-sectional end view of inlet  68 valve stem FIBretention o-ring  69 Head/Bowl Annulus  70 Head Female Threads  71 BowlMale Threads  72 Frit Retention Clip  73 Frit  74 Cavity 4 Passage  75Head/Bowl Annulus to Vent Valve  76 Cavity Passage Bowl Upper Rim  77Head/Bowl O-ring  78 FIB Retention ring Shoulder  79 Head Inner Surface 80 Inlet Port/Inlet Valve Cavity Passage  81 Knob Lock Slot  82a KnobLock Slot  82b Pipeline  83 Sample Line  84 Sample Line Valve  85 SampleProbe  86 Pre-charge Gas Supply  87 Pre-charge Gas Supply Pressure  88Regulator Supply Line  89 4 Way Valve  90 4 Way Valve Port  90a 4 WayValve Port  90b 4 Way Valve Port  90c 4 Way Valve Port  90d Vent toAtmosphere or Safe Area  91 Gas Supply  92 Sample Line  93 Sample Line 94 Analyzer  95 Pressure Regulator  96 Valve Stem Tip Recess  97 Line 98 Line  99 Head/Bowl Annulus to Vent 100 Cavity Passage Head/BowlO-ring 101 O-ring Groove 102 Surface 103 Hole 104 Surface 105 Constantvolume sample cylinder 106 with the flexible isolation barrier linerIn summary, a method of the present invention may comprise the steps of:

a. providing a sample cylinder, having a body having a chamber formedtherein;

b. providing a flexible isolation barrier, and utilizing said flexibleisolation barrier to selectively divide said chamber in fluidimpermiable fashion into first and second cavities;

c. forming a first passage associated with said first cavity forselectively allowing the passage of a sample fluid therethrough;

d. forming a second passage associated with said second cavity forselectively allowing the passage of a pre-charge fluid therethrough;

e. allowing a flow of pre-charged gas through said second passage, so asto urge said isolation barrier toward said first cavity, displacingresidual gas in said first cavity;

f. pressurizing said second cavity via said second passage with apre-charge gas at a pre-determined pressure;

g. flowing a sample gas at said pre-determined pressure though saidfirst passage and into said first cavity;

h. utilizing said flexible isolation barrier, receiving about equalpressure from said pre-charge gas from said second cavity, to preventthrottling of said sample gas entering said first cavity; while

i. providing controlled flow of said sample gas into said samplecylinder by selective venting of said pre-charged gas from said secondchamber, until said said pre-charge gas is depleted from said secondcavity, said flexible isolation barrier conforms to the interior of saidchamber, and said sample gas fills said chamber of said sample cylinder.

The invention embodiments herein described are done so in detail forexemplary purposes only, and may be subject to many different variationsin design, structure, application and operation methodology. Thus, thedetailed disclosures therein should be interpreted in an illustrative,exemplary manner, and not in a limited sense.

1. A sample cylinder, comprising: a body having a chamber formedtherein; a flexible isolation barrier situated within said chamber, saidflexible isolation barrier selectively dividing said chamber into firstand second cavities; an inlet valve associated with said first cavity;and a purge valve associated with said second cavity; whereby, uponallowing a flow of pre-charge gas through said purge valve, saidisolation barrier is urged toward said first cavity, displacing residualgas in said first cavity, with said flexible isolation barrierconforming to the interior of said first cavity; and whereby, uponpressurizing said second cavity via said purge valve with a pre-chargegas at a pressure, and flowing a sample gas through said inlet valve andinto said first cavity, said flexible isolation barrier, receivingpressure from said pre-charge gas from said second cavity, providescontrolled flow of said sample gas into said sample cylinder viaselective venting of said pre-charge gas from said second chamber, untilsaid pre-charge gas is depleted from said second cavity, said flexibleisolation barrier conforms to the interior of said chamber, and saidchamber is filled with said sample gas.
 2. The sample cylinder of claim1, wherein said inlet valve is situated adjacent to said first cavitysuch that when said isolation barrier is urged toward said first cavityby said flow of pre-charge gas through said purge valve, residual gas isdisplaced in said first cavity to said inlet valve.
 3. The method ofsampling a hydrocarbon gas, comprising the steps of: a. providing asample cylinder having a body having a chamber formed therein; b.providing a flexible isolation barrier, and utilizing said flexibleisolation barrier to selectively divide said chamber in fluidimpermeable fashion into first and second cavities; c. forming a firstpassage associated with said first cavity for selectively allowing thepassage of a sample fluid therethrough; d. forming a second passageassociated with said second cavity for selectively allowing the passageof a pre-charge fluid therethrough; e. allowing a flow of pre-charge gasthrough said second passage, so as to urge said flexible isolationbarrier toward said first cavity, displacing residual gas in said firstcavity; f. pressurizing said second cavity via said second passage witha pre-charge gas; g. flowing a sample gas through said first passage andinto said first cavity; h. utilizing said flexible isolation barrier toprevent throttling of said sample gas entering said first cavity; whilei. providing controlled flow of said sample gas into said samplecylinder by selective venting of said pre-charge gas from said secondchamber, until said pre-charge gas is depleted from said second cavity,said flexible isolation barrier conforms to the interior of saidchamber, and said sample gas fills said chamber of said sample cylinder.4. The method of claim 3, wherein in step “e” there is further includedthe step of allowing said flow of pre-charge gas through said secondpassage so as to urge said isolation barrier toward said first cavityand to said inlet valve, displacing residual gas in said first cavity tosaid inlet valve.
 5. The method of claim 4, wherein in step “e” there isfurther included the step of purging any passage upstream of said inletvalve.
 6. The method of claim 3, wherein in step “e” said flexibleisolation barrier is urged by said pre-charge gas to conform to theinterior of said first cavity.
 7. The method of sampling a hydrocarbongas, comprising the steps of: a. providing a sample cylinder having abody having a chamber formed therein; b. providing a flexible isolationbarrier having first and second sides within said chamber; c. forming afirst passage for selectively allowing the flow of a sample fluidtherethrough; d. forming a second passage for selectively allowing theflow of a pre-charge fluid therethrough; e. initiating a flow ofpre-charge gas through said second passage, so as to urge said secondside of said flexible isolation barrier to displace residual gascontacting said first side of said flexible isolation barrier withinsaid chamber, while pre-charging said chamber at a pressure; g.initiating a flow of sample gas at said pressure through said firstpassage and into contact with said first side of said flexible isolationbarrier; h. utilizing said flexible isolation barrier and saidpre-charge gas at said pressure contacting said second side of saidflexible isolation barrier, to prevent throttling of said sample gasentering said first cavity; while i. providing controlled flow of saidsample gas into said sample cylinder by selective venting of saidpre-charge gas, until said pre-charge gas is depleted from said chamber,said flexible isolation barrier conforms to the interior of saidchamber, and said sample gas fills said chamber of said sample cylinder.8. A sample cylinder, comprising: a body having a chamber formedtherein, said body having an inlet passage for receiving a sample gas; aflexible isolation barrier having first and second sides situated withinsaid chamber; said first side of said flexible isolation barrierconformed to contain a sample gas emanating from said inlet passage;said second side of said flexible isolation barrier configured toreceive pressure from a pre-charge gas situated in said chamber;whereby, upon urging said pre-charge gas into said chamber so as tocommunicate with said second side of said flexible isolation barrier,said second side of said flexible isolation barrier is urged to displacesample gas contained by said flexible isolation barrier, so as to form apre-charged cylinder; and whereby, upon flowing sample gas through saidinlet means so as to be contained by said flexible isolation barrier,said sample gas is received in said sample cylinder in controlledfashion by selectively venting said pre-charge gas from said chamber incontrolled fashion.
 9. The sample cylinder of claim 8, wherein saidflexible isolation barrier is formed of polyvinyl fluoride.
 10. A samplecylinder, comprising: a bowl having a chamber formed therein; a headthreadingly engaged to said bowl; a flexible isolation barrier situatedwithin said chamber, said flexible isolation barrier selectivelydividing said chamber into first and second cavities; an inlet valveassociated with said first cavity; and a purge valve associated withsaid second cavity; whereby, upon allowing a flow of pre-charge gasthrough said purge valve, said isolation barrier is urged toward saidfirst cavity, displacing residual gas in said first cavity; and whereby,upon pressurizing said second cavity via said purge valve with apre-charge gas at a pressure, and flowing a sample gas at said pressurethrough said inlet valve and into said first cavity, said flexibleisolation barrier, receiving pressure from said pre-charge gas from saidsecond cavity, provides controlled flow of said sample gas into saidsample cylinder via selective venting of said pre-charge gas from saidsecond chamber, until said pre-charge gas is depleted from said secondcavity, and said first chamber is filled with said sample gas.
 11. Thesample cylinder of claim 10, wherein said inlet valve is formed in saidhead of said sample cylinder.
 12. The sample cylinder of claim 11,wherein there is further provided a passage emanating upstream from saidinlet valve.
 13. The sample cylinder of claim 12, wherein there isfurther provided a purge valve associated with said passage upstreamfrom said inlet valve.
 14. The sample cylinder of claim 10, wherein saidpurge valve is formed in said head of said sample cylinder.
 15. Thesample cylinder of claim 14, wherein said inlet valve is situatedadjacent to said first cavity.
 16. The sample cylinder of claim 15,wherein said inlet valve is formed in said bowl.
 17. The sample cylinderof claim 15, wherein said inlet valve is formed in said head.
 18. Thesample cylinder of claim 10, wherein said flexible isolation barrierforms a container having a mouth having a periphery, and wherein saidmouth engages said head via a retention ring.
 19. The method of purginga sample cylinder of residual gas, comprising the steps of: a. providinga sample cylinder having a chamber formed therein; b. providing aflexible isolation barrier having first and second sides within saidchamber; c. forming an inlet valve adjacent to said chamber forselectively allowing the passage of a sample fluid therethrough; d.forming a second passage for selectively allowing the passage of apre-charge fluid therethrough; e. allowing a flow of pre-charge gasthrough said second passage, so as to urge said second side of saidflexible isolation barrier to displace residual gas contacting saidfirst side of said flexible isolation barrier within said chamber,forming displaced residual gas, urging said displaced residual gasthrough said inlet valve until said flexible barrier has displaced allresidual gas, and said first side of said flexible isolation barrier issituated adjacent to said inlet valve.
 20. The method of claim 19,wherein there is further provided the additional step after step “e.” ofventing a passageway upstream of said inlet valve so as to purge saidupstream passageway of contaminants.
 21. The method of sampling a fluid,comprising the steps of: a. providing a sample cylinder having a chamberformed therein; b. providing a flexible isolation barrier having firstand second sides within said chamber; c. forming an inlet valve adjacentto said chamber for selectively allowing the passage of a sample fluidtherethrough; d. forming a second passage for selectively allowing thepassage of a pre-charge fluid therethrough; e. allowing a flow ofpre-charge gas through said second passage, so as to urge said secondside of said flexible isolation barrier to displace residual gascontacting said first side of said flexible isolation barrier withinsaid chamber, forming displaced residual gas, urging said displacedresidual gas through said inlet valve until said flexible barrier hasdisplaced all residual gas, and said first side of said flexibleisolation barrier is situated adjacent to said inlet valve, whilepre-charging said chamber to a pressure; f. flowing a sample gas at saidpressure through said inlet valve so as to be contained by said firstside of said flexible isolation barrier; g. utilizing said flexibleisolation barrier, and said pre-charge gas at said pressure contactingsaid second side of said flexible isolation barrier, to preventthrottling of said sample gas entering said first cavity; while i.providing controlled flow of said sample gas into said sample cylinderby selective venting of said pre-charge gas, until said pre-charge gasis depleted from said chamber, said flexible isolation barrier conformsto the interior of said chamber, and said sample gas fills said chamberof said sample cylinder.
 22. The method of sampling a hydrocarbon gas,comprising the steps of: a. providing a sample cylinder having a bowlhaving a chamber formed therein and a head removeably engageable to saidbowl; b. providing a flexible isolation barrier situated in saidchamber, and utilizing said flexible isolation barrier to selectivelydivide said chamber in fluid impermeable fashion into first and secondcavities; c. pressurizing said second cavity by flowing a precharge gasthrough a second passage into said second cavity with a pre-charge gasat a pressure; d. flowing a sample gas at said pressure through a firstpassage and into said first cavity; e. utilizing said flexible isolationbarrier, receiving about equal pressure from said pre-charge gas fromsaid second cavity, to prevent throttling of said sample gas enteringsaid first cavity; while f. providing controlled flow of said sample gasinto said sample cylinder by selective venting of said pre-charge gasfrom said second chamber, until said pre-charge gas is depleted fromsaid second cavity, said flexible isolation barrier conforms to theinterior of said chamber, and said sample gas fills said chamber of saidsample cylinder.
 23. The method of claim 22, wherein in step “f” saidflexible isolation barrier is urged by said pre-charge gas to conform tothe interior of said first cavity.
 24. A fluid container, comprising: abody having a chamber formed therein; a flexible isolation barriersituated within said chamber, said flexible isolation barrier havingfirst and second sides; an inlet valve associated with said first sideof said flexible isolation barrier; and a purge valve associated withsaid second side of said flexible isolation barrier; whereby, uponallowing a flow of pre-charge gas through said purge valve, saidisolation barrier displaces fluid situated between said first side ofsaid flexible isolation barrier and said inlet valve; and whereby, uponflowing a sample gas through said inlet valve, said first side of saidflexible isolation barrier forms a barrier to prevent said sample gasfrom mixing with said pre-charge gas, while said second side of saidflexible isolation barrier and said pre-charge gas regulates the flow ofsaid sample gas into said chamber via selective venting of saidpre-charge gas, until said pre-charge gas is depleted from said chamber,said flexible isolation barrier conforms to the interior of saidchamber, and said chamber is filled with said sample gas.
 25. A methodof sampling a gas, comprising the steps of: a. providing a fluidcontainer comprising a body having a chamber formed therein; b.providing an isolation barrier situated within said chamber, saidisolation barrier having first and second sides; c. providing an inletvalve associated with said first side of said isolation barrier; d.providing a purge valve associated with said second side of saidisolation barrier; e. flowing a pre-charge gas through said purge valve,so as to urge said isolation barrier to displace fluid situated betweensaid first side of said isolation barrier and said inlet valve; f.flowing a sample gas through said inlet valve; g. utilizing saidisolation barrier to prevent said sample gas from mixing with saidpre-charge gas, while utilizing said sample gas to urge said isolationbarrier to displace fluid situated between said second side of saidisolation barrier and said purge valve; and h. providing controlled flowof said sample gas into said fluid container by selective venting ofsaid pre-charge gas, until said pre-charge gas is depleted from saidchamber and said sample gas fills said chamber of said fluid container.